Method for changing the shape of a can, and can shaped in this way

ABSTRACT

The invention relates to a method for changing the shape of a can ( 2 ), which can has a can wall, such as a deep-drawn can or a wall-ironed can, the can being positioned in or around a die ( 1 ), which die is provided with a surface with, for example, a relief, embossings or thickened sections, after which the can wall is pressed into the shape of the die by means of at least one jet of a high-pressure medium which is moved along the can wall. According to the invention, a supporting layer ( 3 ), which supports the can wall during the deformation of the can wall, is arranged between the can wall and the die. The invention also relates to a can shaped using the method.

[0001] The invention relates to a method for changing the shape of a can, which can has a can wall, such as a deep-drawn can or a wall-ironed can, the can being positioned in or around a die, which die is provided with a surface with, for example, a relief, embossings or thickened sections, after which the can wall is pressed into the shape of the die by means of at least one jet of a high-pressure medium which is moved along the can wall. The invention also relates to a can shaped using this method.

[0002] A method of this type is known from U.S. Pat. No. 5,794,474 and is known to those skilled in the art by the name “rheoforming”. According to the U.S. document, this method is carried out in the manner described above, the can usually being placed inside a die and a nozzle being fitted into the can in order to press the can wall against the die with the aid of a high-pressure water jet. In this case, an excess pressure of, for example, 30 psi prevails inside the can. The pressure of the water jet when it leaves the nozzle is at least 1000 psi. The water jet is usually moved helically along the can wall. The rheoforming increases the cross section of the can at least locally.

[0003] One drawback of this known method is that, after the operation, a helical imprint in the can is visible if the helical movement of the water jet has a pitch of more than 1 mm.

[0004] Another drawback is that the basic processing time for one steel can is approximately 4-6 seconds per can; the processing time for an aluminum can is shorter. The processing time increases further when the operations of placing the can into and removing it from the die are taken into account. In a machine tool, for instance, with a turning chuck, it is therefore possible to process a maximum of 10 to 15 steel cans per minute for each nozzle. This represents a low speed compared to other machine tools, for example deep-drawing machines.

[0005] It is an object of the invention to provide an improved method for shaping cans using rheoforming.

[0006] Another object of the invention is to provide a method for shaping cans using rheoforming so that the can has a more attractive appearance.

[0007] Yet another object of the invention is to provide a method for shaping cans using rheoforming which is able to process more cans per minute.

[0008] A further object of the invention is to provide a can which has been made using rheoforming and has a more pleasant appearance.

[0009] According to a first aspect of the invention, one or more of these objects is/are achieved with a method of the type described in the introduction in which a supporting layer which supports the can wall during the deformation of the can wall is arranged between the can wall and the die.

[0010] Surprisingly, it has been found that, as a result of this supporting layer being provided, a can appearance which is smooth to the naked eye is obtained, even if a pitch which is larger than normal is selected. This means that a higher production rate can be achieved while nevertheless the desired smooth appearance of the can is retained. It is assumed that the supporting layer prevents local peak loads and has a damping and equalizing action during the local high-pressure deformation of the can wall by the jet of medium acting thereon.

[0011] The supporting layer is preferably formed by a layer of a solid. However, it is also conceivable for the supporting layer to be formed by a layer of high-pressure gas, such as air, between the can wall and the die. A solid provides better support for the can wall.

[0012] Preferably, the supporting layer of a solid is arranged against the can wall, so that the layer supports the can wall as soon as the jet of medium acts thereon, rather than only when the can wall has been pressed onto the die.

[0013] According to an advantageous embodiment of the method, a layer of deformable material with a thickness of at most approximately 3 mm, and preferably with a thickness of approximately 1 mm, is used. Obviously, the optimum thickness is to some extent dependent on the deformability of the layer selected, which is easy to determine in practice. The optimum thickness will also depend on the thickness of the can wall.

[0014] A layer of deformable material made from plastics or rubber is preferably used, since these materials have a good ratio between mass, stretch/reinforcement behavior and hardness for the purpose of obtaining the desired damping and equalizing properties.

[0015] According to a preferred method, a layer of deformable material with a hardness of less than 90 Shore D, preferably with a hardness of between 40 Shore D and 70 Shore D, is used. In this way, it is possible to attain good results in terms of the smoothness of the processed can.

[0016] It has been found that excellent results are obtained if a layer of material with a hardness of approximately 55 Shore D is used.

[0017] The layer of deformable material preferably has a density of between 1000 and 7800 kg/m³, preferably between 2500 and 5000 kg/m³. Excellent results are obtained with a material with a density of approximately 3500 kg/m³.

[0018] The jet of the medium is preferably guided helically along the can wall, the pitch of the helix preferably being at least approximately 1 mm. In this way, higher production rates than has hitherto been customary for the rheoforming of smooth cans are used.

[0019] The pitch is preferably 1.5 to 3 mm, and more preferably 1.5 to 2 mm. In this way, the production rate per nozzle can be doubled.

[0020] When carrying out the method, the expansion of the can preferably amounts to at most approximately 10%. It has been found that if the expansion is greater than this, the action of the supporting layer has little effect on reducing the visibility of the helical groove. It is assumed that, if there is considerable expansion of this nature, the jet of the medium deforms the can wall to such an extent that the supporting and damping action of the layer has an insufficient effect. If large expansions are required, the rheoforming is carried out in a number of passes or steps.

[0021] The expansion is preferably at most 5%. The supporting layer then has a clear effect.

[0022] It is preferable if the method is used when the expansion amounts to at most 2%. The effect of the supporting layer is then optimal.

[0023] Preferably, in the method the high-pressure medium used is a water jet at a pressure of between 3000 and 5000 psi. At this high pressure, it is possible to provide sharp transitions, such as embossings. At a lower pressure, the supporting layer leads to a less sharply defined transition.

[0024] According to a second aspect of the invention, a can is provided which has been produced using the method described above, the can having a surface which is mirror-smooth to the naked eye.

[0025] The invention also provides a can which has been produced according to the method described above, the roughness average of the can wall formed being lower than 0.5, i.e. Ra<0.5.

[0026] The invention will be explained on the basis of an exemplary embodiment and with reference to the drawing.

[0027] The only FIGURE diagrammatically depicts a cross section through a mold and a rheoforming tool which is used to shape a can which has been provided with a supporting layer of material according to the invention.

[0028] In cross section, the figure shows a die 1 in which a can 2 is accommodated. The outside of the can is provided with a supporting layer 3 according to the invention. Via the open side of the can, an elongate rheoforming tool 4 is introduced into the can 2, and this tool is able to execute a helical movement as indicated by the arrow B. The rheoforming tool 4 has a nozzle 5 out of which high-pressure water is sprayed, in the direction of arrow A, in order to shape the can.

[0029] In the die 1 there are recesses 11, 12, and 13 which optionally run all the way around the die. As a result, the rheoforming can be used to apply annular thickened sections, (brand)names and symbols and the like, so that, for example, a name can be seen and felt in relief on the can wall. The die is of two-part or multipart design, so that the can can be accommodated in the die.

[0030] The right-hand half of the figure shows, in cross section, the can 2 with a straight wall and the supporting layer 3 arranged thereon before the rheoforming is carried out. The left-hand half of the figure shows, in cross section, the can wall after the rheoforming.

[0031] Since the supporting layer 3 is provided, helical grooves in the can wall are largely prevented, even with a relatively high pitch of, for example, 1.5 mm or 2 mm. The can remains mirror-smooth to the naked eye.

[0032] The layer thickness may vary and is dependent on the hardness of the material. A suitable layer thickness of plastic is approximately 1 mm with a hardness of approximately 55 Shore D and a density of approximately 3500 kg/m³.

[0033] To obtain sharply defined transitions between, for example, sections of the can wall which have been deformed and those which have not been deformed, the pressure of the water jet is preferably higher than if the supporting layer were not being used. A water pressure of from 3000 to 5000 psi is suitable.

[0034] It has been found that with the method according to the invention and the material layer mentioned above, a can can be shaped twice as quickly by rheoforming while the can wall remains mirror-smooth to the naked eye.

[0035] In addition to the plastics material mentioned, rubber is also suitable as a material for the layer of supporting material, while other materials are also possible. It is also possible for the layer not to be a material, but rather a pressurized medium between the can wall and the die, such as air.

[0036] The method can also be used for a can which is arranged around a die, with the result that the can wall is deformed toward its interior. In this case, however, the deformation must remain small.

[0037] It will be understood that the exemplary embodiment described does not limit the invention. The scope of protection is determined by the claims which follow. 

1. A method for changing the shape of a can, which can has a can wall, such as a deep-drawn can or a wall-ironed can, the can being positioned in or around a die, which die is provided with a surface with, for example, a relief, embossings or thickened sections, after which the can wall is pressed into the shape of the die by means of at least one jet of a high-pressure medium which is moved along the can wall, characterized in that a supporting layer, which supports the can wall during the deformation of the can wall, is arranged between the can wall and the die.
 2. The method as claimed in claim 1, characterized in that the supporting layer is formed by a layer of a solid.
 3. The method as claimed in claim 2, characterized in that the supporting layer of a solid is arranged against the can wall.
 4. The method as claimed in claim 2 or 3, characterized in that a layer of deformable material with a thickness of at most approximately 3 mm is used.
 5. The method as claimed in claim 4, characterized in that a layer with a thickness of approximately 1 mm is used.
 6. The method as claimed in one of the preceding claims, characterized in that a layer of deformable material made from plastics or rubber is used.
 7. The method as claimed in one of the preceding claims, characterized in that a layer of deformable material with a hardness of less than 90 Shore D is used.
 8. The method as claimed in claim 7, characterized in that a layer of material with a hardness of between 40 Shore D and 70 Shore D is used.
 9. The method as claimed in claim 8, characterized in that a layer of material with a hardness of approximately 55 Shore D is used.
 10. The method as claimed in one of the preceding claims, characterized in that a layer of deformable material with a density of between 1000 and 7800 kg/m³, preferably between 2500 and 5000 kg/M³, is used.
 11. The method as claimed in claim 10, characterized in that a layer of material with a density of approximately 3500 kg/m³ is used.
 12. The method as claimed in one of the preceding claims, characterized in that the jet of the medium is guided helically along the can wall.
 13. The method as claimed in claim 12, characterized in that the pitch of the helix is at least approximately 1 mm, preferably 1.5 to 3 mm.
 14. The method as claimed in claimed in claim 12, characterized in that the pitch is 1.5 to 2 mm.
 15. The method as claimed in one of the preceding claims, characterized in that the expansion of the can amounts to at most approximately 10%, preferably at most 5%.
 16. The method as claimed in claim 15, characterized in that the expansion amounts to at most 2%.
 17. The method as claimed in one of the preceding claims, characterized in that the medium used is a water jet at a pressure of between 3000 and 5000 psi.
 18. A can produced using the method as claimed in one of claims 1 to 17, characterized in that the can has a surface which is mirror-smooth to the naked eye.
 19. A can produced using the method as claimed in one of claims 1 to 17, characterized in that the roughness average of the can wall formed is lower than 0.5. 